Interpretive Summary: The red imported fire ant was introduced into the United States in the 1930s and currently infests about 300 million acres. It causes significant economic losses ($6 billion annually) in livestock and agricultural production and poses a serious threat to human health. USDA-ARS scientists at the Center for Medical, Agricultural and Veterinary Entomology (Gainesville, FL), School of Biological Sciences, United Kingdom, and Fundacion Para el Estudio de Especies Invasivas, Argentina, have discovered a new virus infecting the imported fire ant. The virus, SiDNV, represents the first DNA virus discovered in the Formicidae and the first densovirus in the insect order, Hymenoptera. The entire genome was sequenced and characterized. SiDNV is limited to fire ants in Argentina, the location where the U.S. population originated, and may serve as a potential classical biological control agent against the U.S. population.

Technical Abstract:
In an effort to expand and utilize viruses as classical biological control agents, a metatranscriptomic/pyrosequencing approach was used to examine Solenopsis invicta populations collected exclusively in Argentina. A new virus with characteristics consistent with the family Parvoviridae, subfamily Densovirinae was discovered. The virus, tentatively named Solenopsis invicta densovirus (SiDNV), represents the first DNA virus discovered in the Formicidae and the first densovirus in the Hymenoptera. The ambisense genome was 5,280 nucleotides in length and contained structural features common to densoviruses. The genome termini possessed asymmetrically positioned 134 nt inverted terminal repeats, formed hairpin loops, and had transcriptional regulatory elements including CAAT and TATA sites. The positive strand encoded ORFs for non-structural (replicative) protein homologs that included putative functional domains for replication initiators including the DNA-dependent ATPase/helicase associated with DNA replication. The negative strand encoded ORFs for structural (viral capsid) protein homologs and a conserved domain for viral phospholipase A2. Corresponding consensus polyadenylation signals were positioned at the end of the major coding regions on each strand. Phylogenetic analysis based on alignments of predicted NS1 sequences from densoviruses revealed that SiDNV assorts within a separate group along with Acheta domestica densovirus and Planococcus citri densovirus. The United States populations of S. invicta were devoid of SiDNV while it was prevalent (>33% infection rate) in those in Argentina. Thus, SiDNV may potentially serve as a significant biocontrol agent against S. invicta in the United States.